Hydraulic motors and driving systems employing same

ABSTRACT

An hydraulic motor comprises a plurality of rows of pistons and cylinders which rows are selectively drivable by fluid under pressure supplied to the motor to provide for different motor speeds for a given delivery of working fluid to the motor. Nonoperative pistons may be retracted to reduce friction losses between the piston&#39;&#39;s followers and the cam track on which the followers react to rotate the motor rotor. A driving system employing the motor and a variable delivery fluid pump is also provided, the system thus having a plurality of speed ranges including high speed at low torque and low speed at high torque.

Foster et a1. 1

HYDRAULIC MOTORS AND DRIVING SYSTEMS EMPLOYING SAME Inventors: Kenneth William Samuel Foster,

Prestbury; Neil McIntosh Wallace, Stockport; Duncan Kinloch Irons, Cheadle, all of England Renold Limited, Wythenshawe, Manchester, England Filed: Dec. 8, 1972 Appl. No.: 313,253

Assignee:

Foreign Application Priority Data Dec. 9, 1971 Great Britain 57161/71 US. Cl. 60/425, 91/492 Int. Cl. Fl5b 7/04 Field of Search 91/492; 60/425; 417/216 References Cited UNITED STATES PATENTS 5/1939 Alpern 91/492 1 1 Feb. 4, 1975 2,370,526 2/1945 Dorun 60/425 3,006,148 10/1961 Hause 417/216 3,511,131 5/1970 Kress 91/492 Primary Examiner-Edgar W. Geoghegan Assistant ExaminerWilliam F. Woods Attorney, Agent, or Firm-Flynn & Frishauf [57] ABSTRACT An hydraulic motor comprises a plurality of rows of pistons and cylinders which rows are selectively drivable by fluid under pressure supplied to the motor to provide for different motor speeds for a given delivery of working fluid to the motor. Non-operative pistons may be retracted to reduce friction losses between the pistons followers and the cam track on which the followers react to rotate the motor rotor. A driving system employing the motor and a variable delivery fluid pump is also provided, the system thus having a plurality of speed ranges including high speed at low torque and low speed at high torque.

23 Claims, 8 Drawing Figures FATENTED FEB 4W5 SHEET 20F 5 PATENTED 4W5 3,863,447

SHEET 3 BF 5 SIGNAL 7076 764 PRESSURE PATENTED FEB 4 I9 5 SHEET u 0F 5 v mm m2 Rm 9m Em mqm QQM HYDRAULIC MOTORS AND DRIVING SYSTEMS EMPLOYING SAME This invention relates to hydraulic motors, and to systems employing same.

This invention is related to those disclosed in copending US. Pat. application Ser. Nos. 313,271; 304,838; 304,840; and 304,748, all assigned to the same Assignee as the present application.

An object of the present invention is to provide an hydraulic motor having more than one speed for a given delivery of fluid under pressure to the motor.

A further object of the present invention is to provide a driving system including a hydraulic motor of the invention, having more than one speed range.

SUMMARY OF THE INVENTION The present invention broadly provides an hydraulic motor having a rotor comprising at least two rows of pistons and cylinders, and adjustable valve means for supplying fluid under pressure into the cylinders and for allowing it to exhaust therefrom, thereby to drive the pistons and rotate the rotor, the valve means being adjustable between two alternative positions to communicate a pressure fluid inlet and an exhaust fluid outlet of the motor with a greater and a lesser number of said rows of pistons and cylinders thereby to selectively operate said rows of pistons and cylinders to provide for two different motor speeds for a given delivery of working fluid to the motor.

When fluid under pressure is delivered to a lesser number of rows of pistons and cylinders, the motor runs at a higher speed but with a reduced torque output in each case where the delivery of working fluid to the motor remains the same.

The present invention also provides a driving system comprising a variable delivery pump connected to supply fluid under pressure to an hydraulic motor of the invention, and the motor and the pump may be connected in a closed loop hydraulic system including a booster pump to make up the system leakage.

Such a system has two speed ranges depending upon the setting of the valve means.

Preferably, the valve means is adjustable in response to a fluid pressure signal supplied to the motor to operate the motor at one of its two speeds of operation.

The valve means may be adjustable in response to a cessation of said fluid pressure signal supplied to the motor to operate the motor at the other of its two speeds, and in the absence of said fluid pressure signal the valve means may be adjustable by fluid under pressure supplied into said pressure fluid inlet to operate the motor at said other of its two speed.

The valve means may be adjustable to connect the non-operative row or rows of pistons and cylinders with the exhaust fluid outlet.

This arrangement offers simplicity in a number of respects hereinafter detailed in relation to specific embodiments of hydraulic motor according to the invention. If the motor should be required to reverse however, by changing over the pressure fluid inlet and the exhaust fluid outlet, the inoperative row of pistons and cylinders communicating solely with the exhaust fluid outlet is subjected to inlet pressure in the higher speed setting or range during reversal. Also, when the motor is used in a closed-loop hydraulic system including a booster pump to make up system leakage, the exhaust fluid outlet is always at a pressure above atmospheric pressure and therefore the non-operative row of pistons and cylinders pressurized in any event with consequent loss or torque.

In an alternative arrangement according to the invention therefore and in the case where the hydraulic motor of the invention comprises two rows of said pistons and cylinders the valve means is adjustable to communicate said pressure fluid inlet and the exhaust fluid outlet with one of the rows of pistons and cylinders and the other row of pistons and cylinders with a space within the motor casing vented to atmospheric pressure.

Preferably said space is sealed with respect to the outer ends of the pistons and the piston outer ends are subject to the pressure in a further space within the motor casing.

Preferably also, the piston outer ends carry cam followers which normally engage a cam track at least in part bounding said further space, the followers being tethered to the pistons and the pistons being movable to the inner ends of the cylinders to withdraw the followers out of engagement with said track.

Thus the present invention still further provides a driving system comprising a main hydraulic pump connected in a closed-loop to supply fluid under pressure to an hydraulic motor as defined in the preceding paragraph and a booster pump connected to said loop to boost the inlet pressure to said main hydraulic pump, and to pressurize said further space when said other row of pistons and cylinders is non-operative.

In use, said further space may be subject to the pressure above atmospheric pressure to drive the inoperative pistons to the inner ends of their cylinders.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross section of a part of one embodiment of an hydraulic motor according to this invention;

FIG. 2 is a diagram of a part of one embodiment of a driving system according to this invention and incorporating the motor of FIG. 1;

FIG. 3 is a cross section of a part of a further embodiment of an hydraulic motor according to this invention;

FIG. 4 is a cross section on line ZZ in FIG. 3;

FIG. 5 is a partial cross section showing a detail of the construction of the motor shown in FIG. 3;

FIG. 6 is a diagram of a part of a further embodiment of a driving system according to this invention and incorporating the motor of FIGS. 3, 4 and 5;

FIG. 7 is a view corresponding with FIG. 3 of a still further embodiment of an hydraulic motor according to this invention; and

FIG. 8 is a view corresponding to FIG. 1 of a still further embodiment of an hydraulic motor according to this invention.

DETAILED DESCRIPTION OF ILLUSRATED EMBODIMENTS Referring to the accompanying drawings, and first to FIG. 1 the motor is as described in copending patent applications Ser. Nos. 304,838; 304,840; and 304,748, all filed on Nov. 8, 1972 and assigned to the same Assignee as the present application, and with particular reference to FIGS. 4 and 5 of copending patent application Ser. No. 304,838, but with the following exceptions which will alone be described. a valve sleeve 108 replaces the valve block 4a previously described. A linearly displaceable valve member or spool 102 has a land 102C at one end which slides in the bore of the valve sleeve 108. At its opposite end the spool 102 slides in the bore of the tube 103 corresponding with tube 3a previously described. The tube 103 is press fitted in the sleeve 108 but is not located axially thereby. The spool 102 slides on a central fluid conduit or tube 101 which passes co-axially through the tube 103. The tube 101 is supported at one end by the spool 102 and at its opposite end in a bore in the motor casing where the bore of the tube communicates through a side opening 101a with an external fitting 1010 (see FIG. 5) for a conduit 101d for communicating fluid under pressure with the bore of the tube. The bore of the tube 101 opens into a first space 150 defined between one end face, the left hand end face in FIG. 1 of the spool 102, and the casing plug 6 previously described.

The spool 102 is displaceable from a first position shown in FIG. 1, in which it is located against the plug 6, to a second position in which the land l02c engages against the adjacent end of the tube 103. The ports 105 formed by aligning openings in the tube 103, the valve sleeve 108 and the pintle 1 previously described are inclined so as to open to the bore of the tube 103 to one side of the spool 102 when the spool is in its first position.

The two rows of pistons and cylinders are of equal total cylinder capacity.

The motor will be assumed to operate with 9 as the fluid pressure inlet and 14 as the exhaust fluid outlet.

When the spool 102 is in its first position, as illlustrated in FIG. I, the motor operates as previously described with both rows of pistons and cylinders operative and working to drive the motor rotor.

To operate the motor in a single row mode a fluid pressure signal is supplied, equal to the inlet fluid pressure at 9, through the fitting l01c (FIG. 5) to the bore of the tube 101 and then to the space 150. The spool 102 is, in consequence, displaced to its second position. The spool has a circumferential groove 4 which then interconnects all the inlet ports 105 to the left-hand row of pistons and cylinders in FIG. I as well as the outlet ports from these pistons and cylinders with the annular passage 13a and the exhaust fluid outlet 14 via cut-outs 106 in the end of the tube 103 and slots 109 in the valve sleeve 108. The left-hand row of pistons and cylinders is therefore rendered non-operative but fluid under pressure from the pressure fluid inlet 9 is still supplied to the right-hand row of pistons and cylinders as previously described, to operate the motor.

The net flow of working fluid into and out of the cylinders in the left hand row is nil. Hence if working fluid is still supplied to the inlet 9 at the same rate, the motor runs at twice the speed and if the working fluid is still supplied at the same pressure, the torque output of the motor will be approximately one half of what it was with the spool 102 in its first position and the motor running in its double row mode.

The bore of the tube 101 is normally connected through the fitting 101C with the exhaust fluid outlet 14. Under this condition the inlet pressure in the bore of the tube 103 acts on the right-hand end face in FIG. 1 of the spool which is of lesser effective area than its left-hand end face in this figure, to maintain the spool in its first position and to return it to its first position when the bore of the tube 101 is reconnected with the exhaust fluid outlet to change over the operation of the motor from the single-row mode to the doublerow mode.

Four slots 109 are provided in the valve sleeve 108 to communicate the exhaust ports with the exhaust fluid outlet.

The land 1026 carries an O-ring seal 111 in a groove in the land to prevent leakage of pressure fluid escaping past the land and to increase the machining tolerances affecting the concentricity of the spool 102 and the bores of tube 103 and sleeve 108.

A sealing washer 151 is provided in association with the plug 6.

Referring now to FIG. 2, the motor M is connected in a closed-loop hydraulic system with a main pump P by conduits 153 and 154. A booster pump B is provided to make up leakage of working fluid from the closedloop system and communicates with the loop through a conduit 155 and conduits 156 and 157 containing respectively non-return valves 158 and 159. The booster pump boosts the main pump inlet and the exhaust fluid outlet via the non-return valve 158 or 159. No flow occurs through the non-return valve 159 unless the flow in the closed-loop system is reversed, on overun of the motor for example.

The conduit 155 communicates also with a manual or solenoid operated, two position selector valve S. In its right-hand diagrammatically illustrated position (1) the valve S communicates the conduit 155 with the conduit 101d and thus with the bore of the tube 101. The motor then operates in the double-row mode. In its diagrammatically illustrated position (2) the valve S communicates the conduit 101d with the pressure fluid inlet 9 via the conduit 154 and a conduit 160. A fluid pressure signal is therefore supplied to the motor and the motor then operates in its single-row" mode. In the event of overrun a non-return valve 162 in the conduit 160 prevents the spool 102 returning to its first position.

The driving system described with reference to FIG. 2 is suitable for transmitting drive to a driving wheel of a vehicle such as a fork lift truck or an optionally offhighway vehicle. In the double-row" mode the motor produces high torque at low speed for operating in a loaded condition or on rough terrain and in the singlerow" mode the motor produces low torque at high speed for travelling, on the level, or surfaced roads.

With the system described the pistons of the lefthand row of pistons are maintained in following relation with the cam during single-row" operation and some additional drag and frictional losses therefore result during over run or if the motor is reversed since the pistons and cylinders of the inoperative row are then subject to high pressure. However, the system offers the compensating advantage of simplicity particularly where the motor is not required to operate or operate unduly in reverse.

Referring now to FIGS. 3, 4 and 5 the motor is, in this case, again as described in copending applications Ser. Nos. 304,838; 304,840; and 304,748 and with particular reference to FIGS. 7 and 8 of application Ser. No. 304,840 but with the following exceptions which will alone be described if they have not already been described herein with reference to FIG. 1.

A sliding cup 117 has recesses 118 connecting the outlet ports 119 of the left-hand row of pistons and cylinders with the annular space 13a which in turn connects with the exhaust fluid outlet 14. The cup 117 has holes 121 connecting the inlet ports 12a with the bore of a tube 122 which corresponds with the tube 103 previously described with reference to FIG. 1. The cup 117 slides on the outer diameter of the tube 122.

The cup has a boss 125 co-axially press-fitted in a bore in the floor of the cup and the boss has a central bore which slidably receives the tube 101. At its outer periphery the boss has a keyway 124 which receives a tab 123 formed by bending inwardly a portion of the wall of the tube 122 disposed between slots. The tab 123 co-operates with the keyway 124 to prevent rotation of the cup.

The cup 1 17 is shown in its first position corresponding with double-row" operation of the motor, and is displaceable to a second position corresponding with single-row" operation of the motor by a fluid pressure signal supplied along the tube 101 as hereinbefore described. In its second position the cup engages the adjacent end of the tube 122.

The cup has a circumferential groove 126 at its outer diameter defining with the motor casing a second space which interconnects all the inlet and outlet ports 12a and 119 of the left-hand row of pistons and cylinders when the cup is in its second position. The groove 126 is connected with a space 129 between the pintle 1a and the cylinder block 50a which forms the motor rotor, via two sets of drillings 127 and 128 in the pintle, the drillings 127 being plugged at their outer ends with plugs 131 (see FIG. 4).

The porting ring 19a previously described has lengthwise extending grooves 132 in its outer diameter which communicate the space 129 with a space 12% at the opposite end of the porting ring and this space is vented to atmosphere via a drain fitting 130 (see FIG. 5) on the outside of the motor casing.

The space 100 is, in this embodiment, sealed off from the space 12% by a seal 134.

The cup 117 has O-ring seals in grooves at 117a and ll7b respectively.

Referring now to FIG. 6, corresponding parts are indicated by the same references as used herein with reference to FIGS. 2, 3, 4 and 5.

The selector valve s, has two positions (1) and (2) representing the double" and single row modes of operation of the motor, as before Non-return valves 164 and 165 connected between the conduits 153 and 154 respectively select the conduit at inlet fluid pressure, which is then communicated with the conduit 101d via the selector valve S, to cause the motor to operate in its single-row mode. The boost pressure from the pump B is at the same time connected via a conduit 166, a boost pressure relief valve 203, the selector valve S, and a conduit 167 with the space 100 in the motor casing, and the fluid flow returns to tank T via a restriction 206, a non-return pressure relief valve 204 in parallel with the restriction, and a conduit 168. Thus the pressure in the space 100 is determined by the blow-off pressure of the valve 204 when the motor is operating in the single-row mode.

The restrictor 206 is selected such that in the double-row" mode of operation of the motor (S, position (1 the case leakage from space 100 can flow through the conduit 167, the restrictor 206 and the conduit 168 without any significant build-up of pressure in the space 100. In the single-row mode booster pump excess flow is however, arranged to be sufficiently larger than the case leakage flow so that blow-off occurs through the valve 204 and a pressure in excess of atmospheric pressure is generated in the space 100 just sufficient to force back the pistons of the left-hand row of pistons and cylinders to the inner end of their cylinder bores so'th at the roller followers 63 which are tethered to their pistons are withdrawn out of engagement with their cam disc 27. When this occurs, of course, the inoperative pistons and cylinders in the "single-row" mode of operation of the motor are subject only to atmospheric pressure in the space 129, 12%, through which the fluid in the cylinders is ejected to tank T so that a pressure only slightly above atmospheric pressure is required in the space 100 to overcome the centrifugal forces acting on the pistons and the tank T pressure.

The roller followers 63 are mounted in through bores in the pistons which subtend an angle greater than l whereby the roller followers are tethered to the pistons. The roller followers are located axially by wire rings 64,65 extending circumferentially of, and held in grooves in, the cylinder block 500. Instead of the wire rings 64,65 rings mounted on, or formed as part of the motor casing may be used to locate the roller followers axially as described in detail in copending application Ser. No. 304,748.

In the double-row mode of operation the fluid flow from the relief valve 203 is passed by the selector valve S, via the conduit 168 directly to the tank T.

As before, the selector valve S, may be manually or solenoid operated.

The non-return valves 164, 165 may be replaced by a single non-return valve 207 communicating the conduit 101d with the conduit 154 if single-row operation is required only for forward drive.

The selector valve 5,, or for that matter the selector valve S could equally be a spool valve or a rotary valve or a sliding face valve or any other type of valve, or again, a combination of valves to perform the same function as has been described for the selector valve S, or the selector valve S.

The left-hand end section of the selector valve S, could be omitted and the valve 203 connected permanently to the conduit 167. The restriction 206 could also be omitted so that the conduit 167 is connected to the conduit 168 only via the valve 204. In this case the space is permanently pressurised sufficiently to force back the non-operative pistons in their cylinders to ensure their free wheeling.

The selector valve S, or a combination of valves replacing the selector valve s, and performing the same function as the selector valve S, could be designed to restrict the flow into conduit 101,, so that the cup 117 moves slowly when moving from its first position to its second position. This allows the left-hand row of pistons and cylinders to be cut off relatively slowly whilst allowing a temporary progressively reducing leakage past the selector valve and cup 117. This cushions the step capacity change of the motor and allows the pump flow and the motor output shaft speed to be more easily resynchronised to the changed mode of operation of the motor.

The pump P may be a variable delivery pump whereby the motor M may be operated in two speed ranges depending upon the setting of the selector valve 8,. Since the roller followers are withdrawn from contact with the cam disc in the single-row mode of operation friction losses are reduced. There is no trans fer of fluid between the cylinders of the inoperative row of pistons and cylinders. Flow losses are therefore also reduced. The motor may be operated in either mode and in either direction under these conditions.

FIG. 7 shows a modification of the motor described with reference to FIGS. 3, 4 and 5 where the cup 117a replaces the valve block 4a in FIG. 4 of the specification of application Ser. No. 304,840. Elongated openings 1 17b communicate the inlet ports of the right hand row of pistons and cylinders with the bore of the tube regardless of the position of the cup. Slots 117c in the cup communicate the exhaust ports of the right-hand row of pistons and cylinders with the space 13a regardless of the position of the cup. The motor is otherwise as described with reference to FIGS. 3, 4 and 5.

FIG. 8 shows a motor generally as described with reference to FIG. 1 of the specification except that it is extended to four rows of pistons and cylinders instead of two and each row of pistons and cylinders is as described with reference to FIG. 1 of this specification. Parts corresponding with parts previously described and which it is necessary to refer to again in describing the present embodiment will be referred to by the same reference numeral with the suffix d added. However, only the departures in construction from that previously described with reference to FIG. 1 of this specification will now be described in detail and these involve the valve means for supplying fluid under pressure into the cylinders and for allowing it to exhaust therefrom.

In FIG. 8 the valve sleeve 108d and the tube 103d together present four sets of inlet and outlet ports, one set for each of the four rows of pistons and cylinders.

The motor will again be assumed to operate with 9d as the fluid pressure inlet and 14d as the fluid pressure outlet, although these connections can be reversed in order to reverse the motor.

Thus, one of the inlet ports 105d to the first row of pistons and cylinders is indicated, and corresponding inlet ports 300, 301 and 302 are also indicated for the second, third and fourth rows of pistons and cylinders respectively, proceeding from left to right in the drawfhe valve member of spool 102d has a central longitudinal bore which slidably receives a central control rod 303 which passes co-axially through the tube 103d, the rod 303 being supported towards its left-hand end in the bore of the spool 102d and a co-axial bore in the casing plug 6d and towards its opposite end in a bore in the motor casing proper through which the rod can slide so as to be adjustable lengthwise, from outside the motor casing, with respect to the spool 102d and the plug 6d. Suitable packing glands 304 and 305 are provided in the casing and plug respectively to prevent the leakage of pressure fluid along the rod 303.

The rod 303 has an axial drilling or bore 306 which communicates with a radial drilling or bore 307 which normally opens into a first space 150a. The circumferential groove 4d defines a second space between the spool 102d and the motor casing sleeve 108d which communicates with the space 150d through a radial drilling or bore 308 and a stepped axial drilling or bore 309 in the spool 102d having an orifice 310 at its mouth. The drilling 309 houses a first spring-pressed non-return ball valve means 311 which seats on the drilling step.

The high pressure space in the bore of the tube 103d communicates with the space 150d through a stepped axial drilling 312 having an orifice 313 at its mouth. The orifice 313 is identical with the orifice 310. The drilling 312 houses a second spring-pressed non-return ball valve means 314. High pressure fluid in the space 150d is prevented from escaping into the groove 4d by the non-return valve 311.

If the motor is reversed, high pressure fluid from the groove 4d enters the space 150d and is prevented from excaping into the bore of the tube 103d by the nonreturn valve 314. Thus the space 150d is always at high pressure regardless of the direction of rotation of the motor and the high pressure acts on the left-hand end face of the spool 102d exposed in this space.

The drillings 306 and 307 communicate the space 150d with the motor casing d through a passage 315 and the casing 100d is vented to tank through a case drain (not shown). High pressure fluid from the space 150d can therefore leak to the casing through the drillings 306 and 307 so long as the mouth of the drilling 307 is uncovered by the edge 316 of the central longitudinal bore in the valve spool 102d where it opens into the space 150d, and the extent of this leakage is determined by the area of the mouth of the drilling 307 which is uncovered by this metering edge 316.

The mouth of the drilling 307 has an effective area compared with the orifices 313 and 310 such that when the drilling 307 is fully uncovered in the space 15011 the pressure of fluid in the space approaches therefore that of the casing 100d therefore, and the valve spool 102d, which is linearly displaceable, is urged to the left in FIG. 8 either by high'pressure fluid in the bore of the tube 103d acting on the opposite right-hand end face of the spool or by high pressure fluid in the groove 4d acting on the differential area between the right-hand face of the land 102a! and the left-hand face of the right-hand land of spool 102d. Both these faces are of lesser surface area than the left-hand end face of the spool 102d exposed in the space 150d. When the metering edge 316 fully covers the mouth of the drilling 307 the pressure of fluid in the space 150d rises to the inlet pressure and the valve spool 102d is urged to the right in the drawing by the pressure of fluid in the space 150d, acting on the full left-hand end face of the spool. At intermediate positions of the metering edge 316 relative to the mouth of the drilling 307, intermediate pressures are set-up in the space 150d between inlet pressure andd that of the casing 100d and the metering edge 316 on the valve spool 102a will therefore always move to an equilibrium position relative to the drilling 307 in which the fluid pressure forces acting on the valve spool are balanced. The position of the rod 303 therefore always determines the position of the valve spool between its extreme leftand right-hand positions in which the land 102cd engages respectively against the plug 6d and the left-hand end of the tube 103d, the spool following-up the movement of the rod in either direction between these two positions, until it reaches an equilibrium position.

The groove 4d in the present example is long enough to isolate up to three of the rows of pistons and cylinders, that is to say the rows served by the ports 105d, 300 and 301. When isolated by the groove 4d both the inlet ports and outlet ports 350 or 351 or 352 or 353 of a row of cylinders are communicated with the exhaust fluid outlet 14d via the cut outs 106d and the slots 109d.

Movement of the rod 303 to the right in the drawing therefore will cause the valve spool 102d to move to the right to isolate either the first or the first and second or the first, second and third rows of pistons and cylinders, thereby to increase the speed of the motor in steps for a given delivery of fluid under pressure to the fluid pressure inlet of the motor.

A circlip 330 on the rod 303 prevents the mouth of the drilling 307 being closed off in the plug 6d.

The rod 303 may conveniently be positioned in the preset positions necessary to operate the motor with one, two, three or four rows of the pistons and cylinders by means of spring pressed detents engaging in depressions in the surface of the rod.

The motor as described with reference to FIG. 8 may also be connected in a fluid circuit to be driven by a variable delivery fluid pump. In this case a driving system is provided having four speed ranges.

It will be evident that the valve means described with reference to FIG. 8, and the servo arrangement for operating it, may be extended to control the operation of up to more than four rows of pistons and cylinders in an hydraulic motor generally as described. Alternatively, it may be used to control the operation ofjust two rows of pistons and cylinders instead of the valve means as described with reference to FIG. 1 of this specification.

The hydraulic motors which have been described are generally of a known kind comprising an assemblage of rotatable pistons and cylinders, to provide the output drive of the motor, by the action of fluid under pressure supplied into and exhausted from the cylinders through a ring or rings of inlet and exhaust ports in a stationary part of the motor casing, such as have been described. The invention is applied to hydraulic motors of this kind, to provide for at least two different motor speeds for a given delivery of working fluid to the motor, in a manner illustrated in the specific embodiments described with reference to the accompanying drawings.

A motor according to the invention operates as a pump, on onverrun in a closed circuit transmission, and may be used purely as a pump. The invention accordingly includes pumps as well as motors.

The rows of pistons and cylinders are not necessarily of equal total cylinder capacity as has been described or illustrated.

We claim:

1. An hydraulic motor having means for receiving an externally generated fluid pressure signal and having:

a stationary casing having a fluid pressure inlet and an exhaust fluid outlet, said casing comprising a stationary casing part presenting at least two rings of ports;

a rotor comprising at least two rows of pistons and cylinders and rotatable about said stationary casing part, the pistons being reciprocable in their cylinders by the action of fluid under pressure supplied into and exhausted from the cylinders of each row of cylinders respectively through said rings of ports to thereby rotate the rotor; and

adjustable valve means for communicating the pressure fluid inlet and the exhaust fluid outlet with different numbers of said rows of ports, the valve means comprising only a single displaceable valve member which is slideable in said casing so as to be selectively adjustable,

which is oppositely directed to said first effective area of the valve member,

said valve means controlling the supply of the working fluid to the motor by selectively communicating said pressure fluid inlet and an exhaust fluid outlet of the motor respectively with afirst number of said I rows when in a first of said two alternative positions and with a second number of said rows which is greater than said first number of said rows when in the other of said two alternative positions, to provide for two different motor speeds for a given delivery of working fluid to the motor, the pressure fluid inlet and the exhaust fluid outlet being interchangeable to rotate the rotor in opposite directions.

2. An hydraulic motor as claimed in claim 1 wherein the valve means is responsive to a cessation of said fluid pressure signal supplied to the motor to operate the motor at one of said two different motor speeds for said given delivery of working fluid to the motor.

3. An hydraulic motor as claimed in claim 2 wherein in the absence of said fluid pressure signal the valve means is responsive to fluid under pressure supplied into said pressure fluid inlet to operate the motor at said one of said two different motor speeds for said given delivery of working fluid to the motor.

4. An hydraulic motor as claimed in claim 1 wherein the valve means is adjustable to connect the nonoperative row or rows of pistons and cylinders with the exhaust fluid outlet.

5. An hydraulic motor as claimed in claim 1 wherein the valve means is adjustable to connect the nonoperative row or rows of pistons and cylinders with a space within the motor casing vented to atmospheric pressure.

6. An hydraulic motor as claimed in claim 5 wherein said space is sealed with respect to the outer ends of the pistons and the piston outer ends are subject to the pressure in a further space within the motor casing.

7. An hydraulic motor as claimed in claim 6 wherein the piston outer ends carry cam followers which normally engage a cam track at least in part bounding said further space, the'followers being tethered to the pistons and the pistons being movable to the inner ends of the cylinders to withdraw the followers out of engagement with said track.

8. An hydraulic motor as claimed in claim 3 wherein said linearly displaceable valve member is concentric with the axis of rotation of the rotor and is displaceable along said axis, the member defining a first space between one end face of the valve member and the casing, a fluid conduit is provided communicating said first space with the outside of the motor casing for conducting said fluid pressure signal into said space, said valve member being subject to the pressure of fluid in said pressure fluid inlet or said exhaust fluid outlet on a face opposite said one end face of the valve member, which opposite face is of an effective area less than said one end face.

9. An hydraulic motor as claimed in claim 8 wherein the valve member is a valve spool and the valve spool is slidable axially on said conduit which is disposed coaxially with the valve spool.

10. An hydraulic motor as claimed in claim 9 wherein the valve member supports said conduit at one end thereof.

1 1. An hydraulic motor as claimed in claim wherein the valve member defines with the motor casing a second space which is brought into communication with inlet and outlet ports of said row or rows of pistons and cylinders when the valve member is displaced by said fluid pressure signal, thereby to render said row or rows of pistons and cylinders non-operative, and passage means is provided communicating said inlet and outlet ports through said second space with said space within said motor casing which is vented to atmosphere.

12. A driving system comprising a main hydraulic pump connected in a closed-loop to supply fluid under pressure to an hydraulic motor comprising a stationary casing having a fluid pressure inlet and an exhaust fluid outlet, said casing comprising a stationary casing part presenting two rings of ports; a rotor comprising two rows of pistons and cylinders and rotatable about said stationary casing part; the pistons being reciprocable in their cylinders by the action of fluid under pressure supplied into and exhausted from the cylinders of each row of cylinders respectively through said rings of ports thereby to rotate the rotor; and valve means comprising only a single displaceable valve member which is slideable in said casing so as to be adjustable in response to an external fluid pressure signal, linearly, in two opposite directions between two alternative positions to communicate said pressure fluid inlet and said exhaust fluid outlet of the motor alternatively with one and both of said rings of ports to thereby operate said one or both of the rows of pistons and cylinders to provide two different motor speeds for a given delivery of working fluid to the motor, the pressure fluid inlet and the exhaust fluid outlet being interchangeable t o rotate the rotor in opposite directions, said valve means, when adjusted to said first alternative position, communicates said pressure fluid inlet and said exhaust fluid outlet with said one of said rows of pistons and cylinders while communicating the other row of pistons and cylinders with a space within the motor casing vented to atmospheric pressure, said space being sealed with respect to the outer ends of the pistons and the piston outer ends being subject to the pressure in a further space within the motor casing, the piston outer ends carrying cam followers which normally engage a cam track at least in part bounding said further space, the followers being tethered to the pistons and the pistons being movable to the inner ends of the cylinders to withdraw the followers out of engagement with said track, and a booster pump connected to said loop to boost the inlet pressure to said main hydraulic pump, and to pressurize said further space when said other row of pistons and cylinders is nonoperative.

13. A driving system as.claimed in claim 12 wherein the main hydraulic pump is a variable delivery pump.

14. A driving system as claimed in claim l2 wherein the booster pump is connected through a non-return valve into the hydraulic loop on the inlet side of the main hydraulic pump and through a non-return valve into the hydraulic loop on the discharge side of the main hydraulic pump, a two-position selector valve is provided which has one position in which it communicates the discharge side of the pump through a nonreturn valve with said fluid conduit to supply said fluid pressure signal thereto, said selector valve, in its said one position, connecting the booster pump with said further space within the motor casing, the selector valve, in its other position, connecting said fluid pressure conduit with the booster pump which operates at a discharge pressure less than the main hydraulic pump.

15. A driving system as claimed in claim 14 wherein the booster pump supplies boost pressure valve through a boost pressure relief valve to pressurise said further space within the motor casing, and the fluid flow to that space return to tank via a restriction and a non-return pressure relief valve connected in parallel with one another, the restriction being selected such that in said other position of the selector valve the pressure in said further space is substantially relieved, the boost pressure overcoming the leakage flow through said restriction when the selector valve is in its said one position to build up pressure in said further space sufficient to move the pistons to the inner ends of the cylinders and withdraw the followers out of engagement with the cam track as aforesaid.

16. A driving system as claimed in claim 12 wherein the booster pump is connected through a nonreturn valve into the hydraulic loop on the inlet side of the main hydraulic pump and through a non-return valve into the hydraulic loop on the discharge side of the main hydraulic pump, a two-position selector valve is provided which has one position in which it communicates the discharge side of the pump through a nonreturn valve with said fluid conduit to supply said fluid pressure signal thereto, the booster pump being connected with said further space within the motor casing through a boost pressure relief valve, the fluid flow to that space returning to tank via a non-return pressure relief valve, the selector valve in its other position, connecting said fluid pressure conduit with the booster pump which operates at a discharge pressure less than the main hydraulic pump, the boost pump pressure overcoming said non-return pressure relief valve to build up pressure in said further space sufficient to move the pistons to the inner ends of the cylinders and withdraw the followers out of engagement with the cam track as aforesaid.

17. A driving system as claimed in claim 14 wherein said selector valve in its said one position restricts the flow of pressure fluid to said fluid conduit whereby said valve means is adjusted slowly.

18. A driving system comprising a variable delivery pump connected to supply fluid under pressure to an hydraulic motor having a rotor comprising two rows of pistons and cylinders and valve means for supplying fluid under pressure into the cylinders and for allowing it to exhaust therefrom, thereby to drive the pistons and rotate the rotor, the valve means being adjustable responsive to an external fluid pressure signal to communicate a pressure fluid inlet and an exhaust fluid outlet of the motor alternatively with one and both of said rows of pistons and cylinders to thereby operate said one or both the rows of pistons and cylinders to provide two different motor speeds for a given delivery of working fluid to the motor, said motor and said p u mp being connected in closed loop hydraulic system including a booster pump to make up the system leakage, said valve means being adjustable in response to a fluid pressure signal supplied to the motor to operate the motor in one of its two modes of operation, and in response to a cessation of said fluid pressure signal supplied to the motor, to operate the motor in the other of its two modes of operation, the valve means being adjustable, in the absence of said fluid pressure signal, by fluid under pressure supplied into said pressure fluid inlet to operate the motor in said other of its two modes, the valve means comprising a linearly displaceable valve member defining a first space between one end face of the valve member and the motor casing, a fluid conduit being provided communicating said first space into the outside of the motor casing for conducting said fluid pressure signal into said space, said valve member being subject to the pressure of fluid in said inlet or a face opposite said one end face of the valve member which opposite face is of an effective area less than said one end face, and the booster pump is connected through a non-return valve into the hydraulic loop on the inlet side of the variable delivery pump and through a non-return valve into the hydraulic loop on the discharge side of the hydraulic pump, the booster pump being additionally connected through a twoposition selector valve to supply, in one position of said selector valve, said fluid pressure signal to said fluid conduit, the selector valve, in its other position, connccting said fluid conduit with said hydraulic loop between the discharge side of said variable delivery pump and the pressure fluid inlet to the motor via a nonreturn valve.

19. An hydraulic motor as claimed in claim 1 comprising only two rows of pistons and cylinders.

20. An hydraulic motor having means for receiving an externally generated fluid pressure signal and havmg:

a stationary casing having a fluid pressure inlet and an exhaust fluid outlet, said casing comprising a stationary casing part presenting at least two rings of ports;

a rotor comprising at least two rows of pistons and cylinders and rotatable about said stationary casing part, the pistons being reciprocable in their cylinders by the action of fluid under pressure supplied into and exhausted from the cylinders of each row of cylinders respectively through said rings of ports thereby to rotate the rotor;

adjustable valve means for communicating the pressure fluid inlet and the exhaust fluid outlet with different numbers of said rows of ports, the valve means comprising only a single displaceable valve member which is slideable in said casing so as to be selectively adjustable, linearly, in two opposite directions between two alternative positions and in one direction in response to the fluid pressure signal supplied to the motor, said linearly displaceable valve member being concentric with the axis of rotation of the rotor and being displaceable along said axis, said valve member defining a first space between one end face of the valve member and the casing; and

a fluid conduit communicating said first space with the outside of the motor casing for conducting said fluid pressure signal into said space, said valve member being subject to the pressure of fluid in said pressure fluid inlet or said exhaust fluid outlet on a face opposite said one end face of the valve member, which opposite face is of an effective area less than said one end face;

said valve means controlling the supply of the working fluid to the motor by selectively communicating said pressure fluid inlet and said exhaust fluid outlet of the motor respectively with a first number of said rows when in a first of said two alternative positions and with a second number of said rows which is greater than said first number of said rows when in the other of said two alternative positions, to provide for two different motor speeds for a given delivery of working fluid to the motor, said valve means being responsive to a cessation of said fluid pressure signal supplied to the motor to operate the motor at one of said two different motor speeds for said given delivery of working fluid to the motor, and in the absence of said fluid pressure signal the valve means is responsive to fluid under pressure supplied into said pressure fluid inlet to operate the motor at said one of said two different motor speeds, the pressure fluid inlet and the exhaust fluid outlet being interchangeable to rotate the rotor in opposite directions.

21. An hydraulic motor as claimed in claim 20 wherein the valve member is a valve spool and the valve spool is slidable axially on said conduit which is disposed co-axially with the valve spool. I

22. An hydraulic motor as claimed in claim 21 wherein the valve member supports said conduit at one end thereof.

23. An hydraulic motor having means for receiving an externally generated fluid pressure signal and having:

a stationary casing having a fluid pressure inlet and an exhaust fluid outlet, said casing comprising a stationary casing part presenting at least two rings of ports;

a rotor comprising at least two rows of pistons and cylinders and rotatable about said stationary casing part, the pistons being reciprocable in their cylinders by the action of fluid supplied into and exhausted from the cylinders of each row of cylinders respectively through said rings of ports thereby to rotate the rotor; and

adjustable valve means for communicating the pressure fluid inlet and the exhaust fluid outlet with different numbers of said rows of ports, the valve means comprising only a single displaceable valve member which is slideable in said casing so as to be selectively adjustable, linearly, in two opposite directions between two alternative positions and in one direction in response to the fluid pressure signal supplied to the motor;

said valve means controlling the supply of the working fluid to the motor by selectively connecting said pressure fluid inlet and said exhaust fluid outlet of the motor respectively with ti) a first number of said rows when in a first of said two alternative positions and connecting the nonoperative pistons and cylinders with a space 'within the motor casing vented to atmospheric pressure, and (ii) with a second number of said rows which is greater than said first number of said rows when in the other of said two alternative positions, to provide for two different motor speeds for a given delivery of working fluid to the motor;

said valve member defining with the motor casing a second space which is brought into communication with inlet and outlet ports of said row or rows of tions. 

1. An hydraulic motor having means for receiving an externally generated fluid pressure signal and having: a stationary casing having a fluid pressure inlet and an exhaUst fluid outlet, said casing comprising a stationary casing part presenting at least two rings of ports; a rotor comprising at least two rows of pistons and cylinders; and rotatable about said stationary casing part, the pistons being reciprocable in their cylinders by the action of fluid under pressure supplied into and exhausted from the cylinders of each row of cylinders respectively through said rings of ports to thereby rotate the rotor; and adjustable valve means for communicating the pressure fluid inlet and the exhaust fluid outlet with different numbers of said rows of ports, the valve means comprising only a single displaceable valve member which is slideable in said casing so as to be selectively adjustable, linearly, in two opposite directions by fluid under pressure between two alternative positions, said valve member being displaceable in one direction in response to the fluid pressure signal supplied to the motor and acting on a first effective area of the valve member, and being displaceable in the other direction by the supply of working fluid to the motor and acting on a lesser effective area of the valve member which is oppositely directed to said first effective area of the valve member, said valve means controlling the supply of the working fluid to the motor by selectively communicating said pressure fluid inlet and an exhaust fluid outlet of the motor respectively with a first number of said rows when in a first of said two alternative positions and with a second number of said rows which is greater than said first number of said rows when in the other of said two alternative positions, to provide for two different motor speeds for a given delivery of working fluid to the motor, the pressure fluid inlet and the exhaust fluid outlet being interchangeable to rotate the rotor in opposite directions.
 2. An hydraulic motor as claimed in claim 1 wherein the valve means is responsive to a cessation of said fluid pressure signal supplied to the motor to operate the motor at one of said two different motor speeds for said given delivery of working fluid to the motor.
 3. An hydraulic motor as claimed in claim 2 wherein in the absence of said fluid pressure signal the valve means is responsive to fluid under pressure supplied into said pressure fluid inlet to operate the motor at said one of said two different motor speeds for said given delivery of working fluid to the motor.
 4. An hydraulic motor as claimed in claim 1 wherein the valve means is adjustable to connect the non-operative row or rows of pistons and cylinders with the exhaust fluid outlet.
 5. An hydraulic motor as claimed in claim 1 wherein the valve means is adjustable to connect the non-operative row or rows of pistons and cylinders with a space within the motor casing vented to atmospheric pressure.
 6. An hydraulic motor as claimed in claim 5 wherein said space is sealed with respect to the outer ends of the pistons and the piston outer ends are subject to the pressure in a further space within the motor casing.
 7. An hydraulic motor as claimed in claim 6 wherein the piston outer ends carry cam followers which normally engage a cam track at least in part bounding said further space, the followers being tethered to the pistons and the pistons being movable to the inner ends of the cylinders to withdraw the followers out of engagement with said track.
 8. An hydraulic motor as claimed in claim 3 wherein said linearly displaceable valve member is concentric with the axis of rotation of the rotor and is displaceable along said axis, the member defining a first space between one end face of the valve member and the casing, a fluid conduit is provided communicating said first space with the outside of the motor casing for conducting said fluid pressure signal into said space, said valve member being subject to the pressure of fluid in said pressure fluid inlet or said exhaust fluid outlet on a face opposite said one end face of the valve member, which opPosite face is of an effective area less than said one end face.
 9. An hydraulic motor as claimed in claim 8 wherein the valve member is a valve spool and the valve spool is slidable axially on said conduit which is disposed co-axially with the valve spool.
 10. An hydraulic motor as claimed in claim 9 wherein the valve member supports said conduit at one end thereof.
 11. An hydraulic motor as claimed in claim 5 wherein the valve member defines with the motor casing a second space which is brought into communication with inlet and outlet ports of said row or rows of pistons and cylinders when the valve member is displaced by said fluid pressure signal, thereby to render said row or rows of pistons and cylinders non-operative, and passage means is provided communicating said inlet and outlet ports through said second space with said space within said motor casing which is vented to atmosphere.
 12. A driving system comprising a main hydraulic pump connected in a closed-loop to supply fluid under pressure to an hydraulic motor comprising a stationary casing having a fluid pressure inlet and an exhaust fluid outlet, said casing comprising a stationary casing part presenting two rings of ports; a rotor comprising two rows of pistons and cylinders and rotatable about said stationary casing part; the pistons being reciprocable in their cylinders by the action of fluid under pressure supplied into and exhausted from the cylinders of each row of cylinders respectively through said rings of ports thereby to rotate the rotor; and valve means comprising only a single displaceable valve member which is slideable in said casing so as to be adjustable in response to an external fluid pressure signal, linearly, in two opposite directions between two alternative positions to communicate said pressure fluid inlet and said exhaust fluid outlet of the motor alternatively with one and both of said rings of ports to thereby operate said one or both of the rows of pistons and cylinders to provide two different motor speeds for a given delivery of working fluid to the motor, the pressure fluid inlet and the exhaust fluid outlet being interchangeable to rotate the rotor in opposite directions said valve means, when adjusted to said first alternative position, communicates said pressure fluid inlet and said exhaust fluid outlet with said one of said rows of pistons and cylinders while communicating the other row of pistons and cylinders with a space within the motor casing vented to atmospheric pressure, said space being sealed with respect to the outer ends of the pistons and the piston outer ends being subject to the pressure in a further space within the motor casing, the piston outer ends carrying cam followers which normally engage a cam track at least in part bounding said further space, the followers being tethered to the pistons and the pistons being movable to the inner ends of the cylinders to withdraw the followers out of engagement with said track, and a booster pump connected to said loop to boost the inlet pressure to said main hydraulic pump, and to pressurize said further space when said other row of pistons and cylinders is non-operative.
 13. A driving system as claimed in claim 12 wherein the main hydraulic pump is a variable delivery pump.
 14. A driving system as claimed in claim 12 wherein the booster pump is connected through a non-return valve into the hydraulic loop on the inlet side of the main hydraulic pump and through a non-return valve into the hydraulic loop on the discharge side of the main hydraulic pump, a two-position selector valve is provided which has one position in which it communicates the discharge side of the pump through a non-return valve with said fluid conduit to supply said fluid pressure signal thereto, said selector valve, in its said one position, connecting the booster pump with said further space within the motor casing, the selector valve, in its other position, connecting said fluid pressure conduit with the booster pUmp which operates at a discharge pressure less than the main hydraulic pump.
 15. A driving system as claimed in claim 14 wherein the booster pump supplies boost pressure valve through a boost pressure relief valve to pressurise said further space within the motor casing, and the fluid flow to that space return to tank via a restriction and a non-return pressure relief valve connected in parallel with one another, the restriction being selected such that in said other position of the selector valve the pressure in said further space is substantially relieved, the boost pressure overcoming the leakage flow through said restriction when the selector valve is in its said one position to build up pressure in said further space sufficient to move the pistons to the inner ends of the cylinders and withdraw the followers out of engagement with the cam track as aforesaid.
 16. A driving system as claimed in claim 12 wherein the booster pump is connected through a non-return valve into the hydraulic loop on the inlet side of the main hydraulic pump and through a non-return valve into the hydraulic loop on the discharge side of the main hydraulic pump, a two-position selector valve is provided which has one position in which it communicates the discharge side of the pump through a non-return valve with said fluid conduit to supply said fluid pressure signal thereto, the booster pump being connected with said further space within the motor casing through a boost pressure relief valve, the fluid flow to that space returning to tank via a non-return pressure relief valve, the selector valve in its other position, connecting said fluid pressure conduit with the booster pump which operates at a discharge pressure less than the main hydraulic pump, the boost pump pressure overcoming said non-return pressure relief valve to build up pressure in said further space sufficient to move the pistons to the inner ends of the cylinders and withdraw the followers out of engagement with the cam track as aforesaid.
 17. A driving system as claimed in claim 14 wherein said selector valve in its said one position restricts the flow of pressure fluid to said fluid conduit whereby said valve means is adjusted slowly.
 18. A driving system comprising a variable delivery pump connected to supply fluid under pressure to an hydraulic motor having a rotor comprising two rows of pistons and cylinders and valve means for supplying fluid under pressure into the cylinders and for allowing it to exhaust therefrom, thereby to drive the pistons and rotate the rotor, the valve means being adjustable responsive to an external fluid pressure signal to communicate a pressure fluid inlet and an exhaust fluid outlet of the motor alternatively with one and both of said rows of pistons and cylinders to thereby operate said one or both the rows of pistons and cylinders to provide two different motor speeds for a given delivery of working fluid to the motor, said motor and said pump being connected in closed loop hydraulic system including a booster pump to make up the system leakage, said valve means being adjustable in response to a fluid pressure signal supplied to the motor to operate the motor in one of its two modes of operation, and in response to a cessation of said fluid pressure signal supplied to the motor, to operate the motor in the other of its two modes of operation, the valve means being adjustable, in the absence of said fluid pressure signal, by fluid under pressure supplied into said pressure fluid inlet to operate the motor in said other of its two modes, the valve means comprising a linearly displaceable valve member defining a first space between one end face of the valve member and the motor casing, a fluid conduit being provided communicating said first space into the outside of the motor casing for conducting said fluid pressure signal into said space, said valve member being subject to the pressure of fluid in said inlet or a face opposite said one end face of the valve member which oppOsite face is of an effective area less than said one end face, and the booster pump is connected through a non-return valve into the hydraulic loop on the inlet side of the variable delivery pump and through a non-return valve into the hydraulic loop on the discharge side of the hydraulic pump, the booster pump being additionally connected through a two-position selector valve to supply, in one position of said selector valve, said fluid pressure signal to said fluid conduit, the selector valve, in its other position, connecting said fluid conduit with said hydraulic loop between the discharge side of said variable delivery pump and the pressure fluid inlet to the motor via a non-return valve.
 19. An hydraulic motor as claimed in claim 1 comprising only two rows of pistons and cylinders.
 20. An hydraulic motor having means for receiving an externally generated fluid pressure signal and having: a stationary casing having a fluid pressure inlet and an exhaust fluid outlet, said casing comprising a stationary casing part presenting at least two rings of ports; a rotor comprising at least two rows of pistons and cylinders and rotatable about said stationary casing part, the pistons being reciprocable in their cylinders by the action of fluid under pressure supplied into and exhausted from the cylinders of each row of cylinders respectively through said rings of ports thereby to rotate the rotor; adjustable valve means for communicating the pressure fluid inlet and the exhaust fluid outlet with different numbers of said rows of ports, the valve means comprising only a single displaceable valve member which is slideable in said casing so as to be selectively adjustable, linearly, in two opposite directions between two alternative positions and in one direction in response to the fluid pressure signal supplied to the motor, said linearly displaceable valve member being concentric with the axis of rotation of the rotor and being displaceable along said axis, said valve member defining a first space between one end face of the valve member and the casing; and a fluid conduit communicating said first space with the outside of the motor casing for conducting said fluid pressure signal into said space, said valve member being subject to the pressure of fluid in said pressure fluid inlet or said exhaust fluid outlet on a face opposite said one end face of the valve member, which opposite face is of an effective area less than said one end face; said valve means controlling the supply of the working fluid to the motor by selectively communicating said pressure fluid inlet and said exhaust fluid outlet of the motor respectively with a first number of said rows when in a first of said two alternative positions and with a second number of said rows which is greater than said first number of said rows when in the other of said two alternative positions, to provide for two different motor speeds for a given delivery of working fluid to the motor, said valve means being responsive to a cessation of said fluid pressure signal supplied to the motor to operate the motor at one of said two different motor speeds for said given delivery of working fluid to the motor, and in the absence of said fluid pressure signal the valve means is responsive to fluid under pressure supplied into said pressure fluid inlet to operate the motor at said one of said two different motor speeds, the pressure fluid inlet and the exhaust fluid outlet being interchangeable to rotate the rotor in opposite directions.
 21. An hydraulic motor as claimed in claim 20 wherein the valve member is a valve spool and the valve spool is slidable axially on said conduit which is disposed co-axially with the valve spool.
 22. An hydraulic motor as claimed in claim 21 wherein the valve member supports said conduit at one end thereof.
 23. An hydraulic motor having means for receiving an externally generated fluid pressure signal and having: a stationary casing having a fluid pressUre inlet and an exhaust fluid outlet, said casing comprising a stationary casing part presenting at least two rings of ports; a rotor comprising at least two rows of pistons and cylinders and rotatable about said stationary casing part, the pistons being reciprocable in their cylinders by the action of fluid supplied into and exhausted from the cylinders of each row of cylinders respectively through said rings of ports thereby to rotate the rotor; and adjustable valve means for communicating the pressure fluid inlet and the exhaust fluid outlet with different numbers of said rows of ports, the valve means comprising only a single displaceable valve member which is slideable in said casing so as to be selectively adjustable, linearly, in two opposite directions between two alternative positions and in one direction in response to the fluid pressure signal supplied to the motor; said valve means controlling the supply of the working fluid to the motor by selectively connecting said pressure fluid inlet and said exhaust fluid outlet of the motor respectively with (i) a first number of said rows when in a first of said two alternative positions and connecting the non-operative pistons and cylinders with a space within the motor casing vented to atmospheric pressure, and (ii) with a second number of said rows which is greater than said first number of said rows when in the other of said two alternative positions, to provide for two different motor speeds for a given delivery of working fluid to the motor; said valve member defining with the motor casing a second space which is brought into communication with inlet and outlet ports of said row or rows of pistons and cylinders when the valve member is displaced by said fluid pressure signal, thereby to render said row or rows of pistons and cylinders non-operative, and passage means is provided communicating said inlet and outlet ports through said second space with said space within said motor casing which is vented to atmosphere, the pressure fluid inlet and the exhaust fluid outlet being interchangeable to rotate the rotor in opposite directions. 